Brightening of carbon nanotube photoluminescence through the incorporation of sp3 defects

Piao, Yanmei; Meany, Brendan; Powell, Lyndsey R.; Valley, Nicholas A.; Kwon, Hyejin; Schatz, George C.; Wang, YuHuang

doi:10.1038/nchem.1711

Cited by 415 publications

(872 citation statements)

References 33 publications

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“…[46,87] Recently, several methods including oxygen atom doping and sp 3 www.advancedsciencenews.com the quantum yield by reducing the nonradiative recombination rates. [91][92][93] While CNTs have notably small Stokes shifts (see Figure 8e), these could be enhanced through energy transfer of bundled CNTs with progressively smaller bandgaps.…”

Section: Wwwadvopticalmatdementioning

confidence: 99%

Limits of Visibly Transparent Luminescent Solar Concentrators

Yang

Lunt

2017

Advanced Optical Materials

113

100

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surfaces into energy harvesting resources. This new approach to visibly transparent LSCs was developed by exploiting the nature of excitonic semiconductors to optimize the use of this light-exposed surface area without compromising its existing functionality, thereby avoiding the aesthetic tradeoffs that can hinder adoption. Recent work has demonstrated devices that selectively harvest different parts of the solar spectrum including i) ultraviolet (UV) absorption, with massive downconverted luminescence deeper into the NIR (>400 nm) [4] and ii) near-infrared (NIR) absorption, with even deeper luminescence in the NIR. [3] This work has been subsequently followed by a number of other groups. [8][9][10][11][12] In contrast to transparent photovoltaics, which have also been developed to exploit this untapped area, [13][14][15] this new concentrator approach offers an alternative pathway whereby energy is transported optically, offering a simple route to large-area manufacturing, high defect tolerance, angle independent performance, and low-level energy cost. In this progress report we discuss the theoretical limits of transparent LSCs, idealized configurations, scalability, and properties of enabling materials. Operating Principles of LSCsLuminescent solar concentrators operate based on the following mechanisms (see Figure 1a): a portion of solar spectrum is absorbed in a luminescent dye (or "luminophore") [16] embedded in a transparent waveguide. That absorbed solar energy is then re-emitted at another wavelength isotropically in all directions within the waveguide, provided the oscillators are not preferentially oriented. Due to the index of refraction difference between the waveguide and the ambient environment the re-emitted photons are predominately trapped by total internal reflection, causing them to be directed towards the waveguide edges where they can be converted to electrical power in an edge mounted photovoltaic cell. The overall system power conversion efficiency, η LSC , is then given by:where η Opt is the optical efficiency (number of photons reaching the waveguide edge)/(number of photons incident on the waveguide), R is the front face reflection, η Abs is the solar spectrum Visibly transparent solar harvesting surfaces are an exciting new approach to harvesting solar energy around buildings and mobile electronics to improve their efficiency and autonomy without impacting their appearance. The recent demonstration of ultraviolet (UV) and near-infrared (NIR) selective light harvesters have enabled transparent luminescent solar concentrators (LSCs) that boast unparalleled scalability, flexibility, aesthetic quality, and affordability. Consequently, the question of the efficiency limits has emerged in these new systems. In this perspective, the theoretical efficiency limits of these concentrator systems are reviewed and practical considerations are outlined to approach these limits. For UV and UV/NIR selective harvesting single-junction transparent LSCs are constrained thermodynamically to 21%, which i...

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Section: Wwwadvopticalmatdementioning

confidence: 99%

Limits of Visibly Transparent Luminescent Solar Concentrators

Yang

Lunt

2017

Advanced Optical Materials

113

100

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“…Two-photon techniques or applying magnetic field may provide a means to detect them, as what had been done to observe dark excitons in CNTs [38,39]. In particular, because the double-resonant picture holds better for tBLG with small twist angles due to the better e-h band symmetry, we expect the lifetime of optical excitations in tBLG will be much longer than that in graphene and BLG; the corresponding decay of optical currents shall become longer as the twist angle is reduced.…”

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confidence: 99%

Strongly bound excitons in gapless two-dimensional structures

et al. 2014

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Common wisdom asserts that bound excitons cannot form in high-dimensional (d>1) metallic structures because of their overwhelming screening and unavoidable resonance with nearby continuous bands. Strikingly, here we illustrate that this prevalent assumption is not quite true. A key ingredient that has been overlooked is that of viable decoherence that thwarts the formation of resonances. As an example of this general mechanism, we focus on an experimentally relevant material and predict bound excitons in twisted bilayer graphene, which is a two-dimensional gapless structure exhibiting metallic screening. The binding energies calculated by first-principles simulations are surprisingly large. The low-energy effective model reveals that these bound states are produced by a unique destructive coherence between two alike subband resonant excitons. In particular, this destructive coherent effect is not sensitive to the screening and dimensionality, and hence may persist as a general mechanism for creating bound excitons in various metallic structures, opening the door for excitonic applications based on metallic structures.Bound excitons, electron-hole (e-h) pairs, are of particular interest because of their neat physics picture and intrinsic long lifetime that makes broad applications, including photovoltaic and photocatalytics [1][2][3]. However, the formation of bound e-h pairs had been thought to be impossible in metallic (gapless) systems due to their overwhelming screening effects. Moreover, e-h pairs in gapless structures tend to hybridize with continuous transitions nearby, forming resonant states, whose intrinsic lifetime is substantially shorter. To date, the only exception was found in metallic carbon nanotubes (mCNTs), in which the depressed one-dimensional (1D) screening together with the unique optical symmetry gap lead to the formation of a bound e-h pair [4][5][6][7][8]. Meanwhile, these studies ignite many obvious but fundamental questions: besides 1D metals, can we observe bound excitons in structures with stronger dielectric screening, e.g., higher dimensional (d>2) gapless materials? In addition to the symmetry-related reason revealed in mCNTs, are there any other general mechanisms responsible for bound exciton formation in gapless systems?

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“…The lack of a photoresponse could result from a limited absorptivity for the excitation light, the quenching of emission by surface impurities/defects on the host, and/or an improper orientation towards the host surface. 32 However, based on energy-gap theory 33 and literature reports on CNTs 34 and complexes of ruthenium and other late transition metals, 35 we conclude that it more likely is due to nonradiation relaxation, because the CNT host can be regarded as an extension of the phenanthroline moiety. The increased distance between the electron donor and acceptor lowers the triplet state, but it also increases the probability of vibrational matching between the luminescent state and S 0 .…”

Section: Resultsmentioning

confidence: 88%

Photomagnetic Carbon Nanotubes at Ambient Conditions

et al. 2015

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KEYWORDSbis(2,2-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II), carbon nanotube, diazotization, photoinduced charge transfer, photomagnetism ABSTRACT Bis(2,2-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II) (Ru(bpy) 2 (phen-NH 2 ) 2+ ), an MLCT complex, has a long-lived triplet state in water (λ ex :473 nm; λ em : 620 nm; τ = 615 ns; Φ = 1 relative to that of Ru(bpy) 3 2+ ) and a structure analogous to Ru(bpy) 3 2+ . When Ru(bpy) 2 (phen-NH 2 ) 2+ was subjected to diazotization in the presence of carbon nanotubes (CNTs), it formed nanodots on the CNTs, rendering the resulting tubes (Ru@CNT) capable of transducing photo stimuli (473 nm) into electricity and magnetism at ambient conditions. The increased functionality was highly reproducible, as evidenced by conductive-mode AFM, vibrating sample magnetometry (VSM), and AC susceptibility analysis. The local magnetism probing of the Ru@CNT with magnetic-mode AFM techniques (MFM) indicated that the magnetism originated from the unpaired electrons formed on the photoexcited nanodots. The resulting phase shift behaved as a function of the luminous power and the voltage (V b ) of the electrical bias applied to the Ru@CNT. The V b dependence deviated from the expected quadratic correlation, confirming that the formation of the photoinduced charge separation state at the nanodots is responsible for the photomagnetism. The Ru@CNT tubes showed mobility toward external magnets (65 Gauss) when floating on water and under 473-nm illumination.The Ru@CNT thus appears to be a multifunctional material that might be useful in spintronics.

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Brightening of carbon nanotube photoluminescence through the incorporation of sp3 defects

Cited by 415 publications

References 33 publications

Limits of Visibly Transparent Luminescent Solar Concentrators

Limits of Visibly Transparent Luminescent Solar Concentrators

Strongly bound excitons in gapless two-dimensional structures

Photomagnetic Carbon Nanotubes at Ambient Conditions

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